Recently, there has been increased an interest in forest resources that can be continuously used as industrial raw materials, instead of fossil resources, such as petroleum, coal and the like, which have been predicted to be depleted. Such a forest resource, i.e., a lignocellulose resource, is composed of hydrophilic carbohydrates, such as cellulose, hemicellulose and the like, and a hydrophobic lignin (polyphenol), which form the interpenetrating network (IPN) structure and an complicated complex in the cell wall. The lignocellulose resource imparts useful properties to various materials, because of the structure of the complex.
Two methods are known for utilizing the known lignocellulose resource, i.e. timber. One is a direct utilization of the lignocellulose material by cutting or machining the lignocellulose resource, i.e., the complex itself, and processing it into construction materials or furniture building materials having a predetermined shape, or processing the lignocellulose resource into chips or fibers for manufacturing molded products. The other is an indirect utilization of the lignocellulose material by extracting only cellulose, a component of the complex, and making a pulp of the product.
In view of the expected depletion of fossil resources in the future, the reuse of lignocellulose resources is important in the both utilization forms.
However, in the current situation, if a construction material is prepared according to the direct utilization method, it will have a predetermined shape and be comparatively large; therefore, treatments such as grinding and finely-dividing are usually necessary to reuse the construction material. In addition, thermosetting resins used in molded products are difficult to separate from wood chips and fibers. Therefore, in the direct utilization form, after the first use, a portion of the lignocellulose resource is discarded, in many cases without reuse.
Moreover, in the indirect utilization form, only cellulose is recovered and utilized to make a fiber or sheet.
Similarly, in the direct utilization form, the entire lignocellulose resource, i.e., cellulose and lignin, are not reused and, also in the indirect utilization form, lignin, which is one component of the lignocellulose resource, may be reused or not reused under in certain circumstances.
Lignin is an organic substance that exists in large amounts intermingled with cellulose. The present inventor considered the function of lignin as a complex constituting material and previously filed two applications that are directed to extraction of lignin from the lignocellulose resource in a functionalized form. The first application is Japanese Application No. 1-55686 (JP-A 2-233701) and the second application is Japanese Application No. 8-92695 (unpublished as of the filing date of this corresponding International application). The first application teaches methods of bonding a phenol derivative to the lignocellulose resource and, thereafter, contacting the lignocellulose resource with sulfuric acid, whereby lignin is separated from cellulose, because lignin has a bound phenol derivative. In addition, the second application teaches processes for manufacturing a novel cellulose-lignin molded product by using the hybrid lignin, which was provided in the first application, as a binder for a molded cellulose material.